[R] Help with gamm errors

[Simon Wood]

Rob,

Thanks for sending the example...
>
> m1=gamm(present~s(week,bs="cc")+s(week,bs="cc",by=y1),random=list(garden=~1
>) ,
>   correlation=corAR1(form=~1|garden),family=binomial,data=count.data2)
>
> (ie removing the week term). This model proceeds - to a point...
>
>  Maximum number of PQL iterations:  20
> iteration 1
> iteration 2
> iteration 3
> iteration 4
> iteration 5
> iteration 6
> Error: attempt to select less than one element

-- this relates to the fact that `gamm' assumes that the correlation structure 
is nested within the random effect grouping structure, so in fact the 
`|garden' in the correlation formula is redundant (see ?gamm on correlation). 
Clearly this should be dealt with more gracefully... I'll try to do so for 
the next release. In the meantime just remove the redundant grouping factor. 

best,
Simon

>
> Traceback() suggests that the model fits, but that lme can't calculate
> something?
>
> 2: extract.lme.cov2(ret$lme, mf, n.sr + 1)
> 1: gamm(present ~ s(week, bs = "cc") + s(week, bs = "cc", by = y1),
>        random = list(garden = ~1), correlation = corAR1(form = ~1 |
>            garden), family = binomial, data = count.data2)
>
> Question 2: Any hints on what might be causing this? Am I fitting the wrong
> (or too complicated a model)?
>
> Btw if it is relevant I am using mgcv_1.3-19 and R 2.3.1.
>
> Many thanks for any hints on where I should start digging
> Cheers
> rob
>
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-- 
> Simon Wood, Mathematical Sciences, University of Bath, Bath, BA2 7AY UK
> +44 1225 386603  www.maths.bath.ac.uk/~sw283